The spatial orientation functions of the vestibular system, although clinically relevant, have received little attention compared to reflexes. In the proposed experiments, we intend to characterize the vestibular system's involvement in maintaining spatial constancy for movement planning as humans and primates are passively rotated or translated in three-dimensional (3D) space. This process, referred to as 'visuospatial updating'utilizes extra-retinal signals related to the intervening movement in order to change the end-goal of sensorimotor transformations for eye, hand or limb movements. Although vestibular signals have an important role in this process, spatial constancy has been mostly studied with saccadic ocular deviations, whereas little is currently known about the role of other sources of extra-retinal information. Thus, the long-term goal of these studies is to characterize the functional properties and neural basis for subcortical extra-retinal signals on spatial constancy, with a particular focus on vestibularly-driven mechanisms. Here we propose a series of behavioral and neurophysiological aims to characterize the vestibular system's involvement in visuospatial updating during memory-guided eye movements. Specifically, we will quantify the properties of these processes, as they relate to the numerous computational issues encountered when three-dimensional (3D) vestibular information must be combined with a two-dimensional (2D) retinotopic goal for a saccade. To investigate the neural basis of these interactions, we also propose to characterize visuospatial updating and vestibular memory-contingent saccades after reversible inactivation of each 1 of the 3 cortical eye fields, the lateral intraparietal area (LIP), the frontal eye fields (FEF) and the supplementary eye fields (SEF). Finally, we will also start characterizing the neural correlates of this function by testing whether visual receptive fields of LIP neurons shift during an imposed rotational/translational movement, similarly as previously shown for saccadic eye movements. The proposed studies aim at filling an important gap in knowledge and are fundamental in establishing a causal role for the vestibular system in spatial and sensorimotor functions that, although largely uncharacterized, are important for understanding and treating cognitive deficits of spatial perception.